Conventionally, a display panel of a so-called active matrix driving method constituted by a thin film transistor (hereinafter also referred to as a “TFT”) over a glass substrate is known. As well as a manufacturing technique of a semiconductor integrated circuit, this display panel needs a step of patterning a thin film such as a conductor, a semiconductor, or an insulator by a light-exposure step using a photomask.
A size of a mother glass substrate used for manufacturing a display panel is enlarged from 300 mm×400 mm of the first generation in the early 1990s to 680 mm×880 mm or 730 mm×920 mm of the fourth generation in 2000. Furthermore, the manufacturing technique made such a development that a number of display panels can be obtained from one substrate.
When a size of a glass substrate or a display panel is small, patterning can be carried out comparatively easily by using a photolithography machine. However, as a substrate size is enlarged, an entire surface of a display panel cannot be simultaneously treated by carrying out light-exposure treatment once. Consequently, it is necessary to divide a region where a photoresist is applied into a plurality of block regions and to carry out light-exposure treatment on every predetermined block regions. As for light-exposure treatment, a method for exposing an entire surface of a substrate to light by sequentially repeating the treatment has been developed (for example, see Reference 1: Japanese Patent Application Laid-Open No. Hei 11-326951 and 2: U.S. Pat. No. 6,291,136 B1).